Magnetic motion sensor

ABSTRACT

A magnetic motion sensor, having a mobile magnet ( 3 ) that generates an essentially homogeneous magnetic field (B) with a magnetic-field direction, and having a coupling element ( 6, 6 ′) which is arranged stationary inside the magnetic field (B), a motion-dependent physical quantity (I, F, M) being induced in the coupling element ( 6, 6 ′) when the magnet ( 3 ) moves perpendicular to the magnetic-field direction, and the induced quantity (I, F, M) being measured and output by a sampling element ( 7, 8, 8 ′)

FIELD OF THE INVENTION

[0001] The present invention relates to a magnetic motion sensor, havinga magnet that generates an essentially homogeneous magnetic field with amagnetic-field direction, and having a coupling element which isarranged inside the magnetic field.

[0002] Motion sensors of this type are widely known. They are used tomeasure a motion-dependent physical quantity. In this context, the termmotion-dependent physical quantity is intended to mean a physicalquantity which—unlike a position-dependent physical quantity—depends onthe motion per se.

[0003] In the prior art, the magnet is in this case arranged stationary.The coupling element is mobile. When the coupling element movesperpendicular to the magnetic-field direction, the motion-dependentphysical quantity is induced in the coupling element. The inducedquantity is measured and output by a sampling element.

[0004] Magnetic motion sensors of this type are described, for example,in Gevatter: “Handbuch der Mess-und Automatisierungstechnik” [Handbookof measurement and automation technology], Springer-Verlag, 1999, pages107f and 115. Ferraris sensors are also constructed in this way.

[0005] Owing to the motion of the coupling element, only contactlesssampling of the motion-dependent physical quantity is possible. Themagnetic motion sensors of the prior art therefore need to be adjustedprecisely. For this reason, they are complicated, susceptible tointerference and comparatively expensive.

[0006] It is an object of the invention to provide a more simplyconstructed motion sensor which is robust and not susceptible tointerference.

[0007] The object is achieved in that the magnet is mobile and thecoupling element is stationary.

[0008] The advantage is that the sampling element can then be directlyconnected mechanically to the coupling element. Contactless sampling ofthe coupling element is not necessary. Nevertheless, contactlesssampling of the coupling element is simplified since, because of thestationary coupling element, no shaking, for example, of the couplingelement can occur.

[0009] The motion of the magnet may be translational or rotational,according to requirements.

[0010] The motion-dependent physical quantity may be a force or moment,or a current.

[0011] Further, the motion-dependent physical quantity may beproportional to velocity or acceleration, according to requirements.

[0012] The structural design of the magnetic motion sensor can be madeparticularly simple by the following measures:

[0013] the magnet is designed as a permanent magnet,

[0014] the coupling element is designed as a solid body,

[0015] the coupling element is designed as an electrically conductiveelement.

[0016] Further advantages and details can be found in the followingdescription of an exemplary embodiment, for which the figuresschematically show the following:

[0017]FIG. 1 a side view of a magnetic motion sensor,

[0018]FIG. 2 a plan view of the motion sensor in FIG. 1, and

[0019]FIG. 3 a plan view of another motion sensor.

[0020] According to FIG. 1, a magnetic motion sensor has a sensorhousing 1. The sensor housing 1 is firmly connected to a working-elementhousing 2 of a working element.

[0021] A permanent magnet 3 is mounted in the sensor housing 1. Thepermanent magnet 3 is in this case mounted in such a way that it canrotate about an axis of rotation 4. The permanent magnet 3 generates anessentially homogeneous magnetic field B, which extends parallel to theaxis of rotation 4. The permanent magnet 3 is interlocked in rotationwith a shaft 5 (or alternatively an axle 5) of the working element whoserotational movement is to be measured.

[0022] A stationary coupling element 6, 6′ is also arranged in thesensor housing 1. According to FIG. 1, the coupling element 6, 6′ is inthis case arranged inside the magnetic field B.

[0023] When the shaft 5 or the axle 5 rotates, the permanent magnet 3executes a rotational motion. The motion of the permanent magnet 3 ishence a rotational motion and, specifically, perpendicular to themagnetic-field direction. Consequently, a motion-dependent physicalquantity is induced in the coupling element 6, 6′. This quantity ismeasured and output by sampling elements 7, 8, 8′.

[0024] According to FIG. 2, the coupling element 6 may consist, forexample, of a diamagnetic or paramagnetic metal. In this case, thecoupling element 6 is designed as a solid body and as an electricallyconductive element. The coupling element 6 may in this case be designed,according to requirements, as a comparatively narrow metal striparranged centrally with respect to the axis of rotation 4 or as a(substantially or completely) solid disk.

[0025] Owing to the motion of the permanent magnet 3, a force is exertedon the charge carriers of the coupling element 6, namely the Lorentzforce. Displacement of the freely mobile electrons of the couplingelement 6, which just compensates for the Lorentz force, consequentlytakes place between the axis of rotation 4 and the outer edge of thecoupling element 6.

[0026] The Lorentz force is proportional to the velocity with which thepermanent magnet 3 moves. The velocity of the permanent magnet 3 is inturn proportional to the angular velocity with which the permanentmagnet 3, i.e. the shaft 5 or the axle 5, rotates. An opposing voltage Uthat builds up is hence also proportional to the (rotational) velocityof the permanent magnet 3. If the permanent magnet 3 is accelerated,then its velocity changes and the opposing voltage U that builds up alsochanges. This induces a compensating current I in the coupling element 6because of the charge-carrier displacement that results. Thecompensating current I is proportional to the (rotational) accelerationof the permanent magnet 3. It can be measured, or tapped, using thesampling element 7, e.g. a magnetoresistive sensor 7.

[0027] Further, as an alternative or in addition, it is also possible toarrange an electric dipole 6′, off-center with respect to the axis ofrotation 4, as the coupling element 6′. In this case as well, a force Fis exerted on the charge carriers of the dipole 6′ as a result of therotational motion of the permanent magnet 3. This force F can bemeasured directly via piezoelectric elements 8, 8′ and converted into apiezoelectric voltage U′. As an alternative to measuring the force F, itis also possible to measure a moment M about a dipole axis 9. Thepiezoelectric elements 8, 8′, which in this case represent the samplingelements 8, 8′, are likewise directly connected mechanically to thecoupling element 6′.

[0028] The structure of a magnetic motion sensor for measuring arotational motion of the permanent magnet 3 has been described above inconjunction with FIGS. 1 and 2. The arrangement according to FIGS. 1 and2 can also, however, be readily adapted for a translational motion. Anarrangement of this type is diagrammatically represented in FIG. 3.Those elements which are the same are in this case denoted by the samereference numbers. It is merely necessary to take care that thepermanent magnet 3 is large enough to measure the full movement range tobe traveled in translation.

1. A magnetic motion sensor, having a mobile magnet (3) that generatesan essentially homogeneous magnetic field (B) with a magnetic-fielddirection, and having a coupling element (6, 6′) which is arrangedstationary inside the magnetic field (B), a motion-dependent physicalquantity (I, F, M) being induced in the coupling element (6, 6′) whenthe magnet (3) moves perpendicular to the magnetic-field direction, andthe induced quantity (I, F, M) being measured and output by a samplingelement (7, 8, 8′).
 2. The motion sensor as claimed in claim 1,characterized in that the motion of the magnet (3) is a translationalmotion.
 3. The motion sensor as claimed in claim 1, characterized inthat the motion of the magnet (3) is a rotational motion.
 4. The motionsensor as claimed in claim 1, 2 or 3, characterized in thatmotion-dependent physical quantity (I, F, M) is a force (F) or a moment(M).
 5. The motion sensor as claimed in claim 1, 2 or 3, characterizedin that motion-dependent physical quantity (I, F, M) is a current (I).6. The motion sensor as claimed in claim 1, characterized in that inthat motion-dependent physical quantity (I, F, M) is proportional tovelocity.
 7. The motion sensor as claimed in claim 1, characterized inthat in that in that motion-dependent physical quantity (I, F, M) isproportional to acceleration.
 8. The motion sensor as claimed in claim1, characterized in that the magnet (3) is designed as a permanentmagnet (3).
 9. The motion sensor as claimed in claim 1, characterized inthat the coupling element (6, 6′) is designed as a solid body (6, 6′).10. The motion sensor as claimed in claim 1, characterized in that thecoupling element (6, 6′) is designed as an electrically conductiveelement (6).
 11. The motion sensor as claimed in claim 1, characterizedin that the sampling element (7, 8, 8′) is mechanically connected to thecoupling element (6, 6′).